Increase in frictional resistance due to roughness on a surface is an important issue in, for example, improving the performance of ships or designing piping and flow channels. The surface roughness of a rough surface is considered as the main cause of an increase in frictional resistance. Since old times, efforts have been made to predict an increase in frictional resistance based on surface roughness. General methods which estimate an impact of surface roughness of an inside surface of a pipe involve Moody diagrams or Colebrook equation as described in Non Patent Document 1. Although such methods can be applied to fluids having various flow velocities or various viscosities, the range of roughness wavelengths which can be studied is limited because of the fact that the surface that is evaluated is rendered rough by the attachment of sand grains and therefore the roughness wavelengths are dependent on the grain size of the sand grains. Further, these methods using Moody diagrams or Colebrook equation only take into consideration a relationship between the pipe diameter and the relative roughness height, and neglect profile parameters such as roughness wavelength. On the other hand, methods described in Patent Document 1 and Non Patent Document 2 are used to study the roughness on hulls. The methods of these documents focus on the roughness wavelength and calculate the ratio of the increase in frictional resistance based on a relationship of the square of roughness height and the roughness wavelength. However, the relationship that is studied in these documents assumes that the flow velocity is constant, with no attentions being paid to friction at various flow velocities. In practice, the resistance offered by roughness is increased to various degrees depending on the flow velocity (the speed of a ship or the flow rate in a pipe). Thus, the increase in resistance needs to be calculated at each of the expected flow velocities. However, none has disclosed a method which can predict how much a rough surface with various roughness wavelengths will increase the frictional resistance when in contact with a fluid at various flow velocities, with high accuracy based on surface roughness.